STP Advanced STP 2 — Questions and Answers
Question 1: What is Per-VLAN Spanning Tree (PVST+)?
- Cisco protocol running a separate STP instance for each VLAN, allowing per-VLAN load balancing (Correct answer)
- A single spanning tree for all VLANs
- An STP replacement
- A VLAN creation tool
Correct answer: Cisco protocol running a separate STP instance for each VLAN, allowing per-VLAN load balancing
PVST+ creates a unique spanning tree for each VLAN, enabling different root bridges and traffic paths per VLAN.
Question 2: What is root guard in STP?
- A feature preventing a port from becoming a root port, protecting the root bridge election (Correct answer)
- Physical security for the root bridge
- A password for root access
- A backup root bridge mechanism
Correct answer: A feature preventing a port from becoming a root port, protecting the root bridge election
Root guard ensures that specific ports cannot be elected as root ports, preventing external switches from becoming the root bridge.
Question 3: What is loop guard in STP?
- A feature that prevents alternate or root ports from transitioning to designated/forwarding if BPDUs stop arriving (Correct answer)
- A physical loop prevention device
- A cable management feature
- An IP routing loop prevention
Correct answer: A feature that prevents alternate or root ports from transitioning to designated/forwarding if BPDUs stop arriving
Loop guard prevents a port from erroneously moving to forwarding state when it stops receiving BPDUs, which could create a loop.
Question 4: How does STP handle unidirectional link failures?
- Through features like UDLD (Unidirectional Link Detection) and loop guard (Correct answer)
- STP cannot detect unidirectional failures
- By increasing the hello timer
- Through manual intervention only
Correct answer: Through features like UDLD (Unidirectional Link Detection) and loop guard
Unidirectional link failures are particularly dangerous for STP because one switch may not receive BPDUs while the other sends them normally.
Question 5: What is the recommended practice for STP root bridge placement?
- Place the root bridge on a high-performance core switch central to the network (Correct answer)
- Any switch can be root bridge without consequence
- Place it on an edge switch
- The root bridge does not matter
Correct answer: Place the root bridge on a high-performance core switch central to the network
The root bridge should be a centrally located, high-performance switch to optimize traffic paths and minimize spanning tree depth.
Question 6: What is the purpose of STP portfast?
- To immediately transition access ports to forwarding state, skipping listening and learning (Correct answer)
- To make ports faster
- To prioritize certain ports
- To block unused ports
Correct answer: To immediately transition access ports to forwarding state, skipping listening and learning
PortFast allows access layer ports connected to end devices to begin forwarding immediately without the normal STP delay.
STP Advanced STP 2
What is Per-VLAN Spanning Tree (PVST+)?